Introduction

Sustainability itself simply means that whatever is being considered has the capacity for continuance. Environmental sustainability requires the maintenance of important environmental functions and the natural capital which generates them, where important environmental functions may be considered to be those that are not substitutable, those whose loss is irreversible and is likely to lead to ‘immoderate’ losses (i.e. costs considerably greater than the costs of maintaining the functions), and those that are crucial for the maintenance of health, for the avoidance of substantial threats (such as climate instability) and for economic sustainability.